1. Field of the Invention
The present invention relates to a method for controlling the exposure amount of duration during photographic printing for purposes of obtaining a photographic print of proper printing density even where the original is a negative film which possesses a subjective density failure. More particularly, the present invention relates to a method for controlling the exposure amount based on the difference in characteristic values (average transmission density, highest density, lowest density, and a combination of these) between portions of the original obtained by dividing the scene of a negative film.
2. Description of the Prior Art
Illustrative examples of prior art exposure control methods are provided in U.S. patent application Ser. No. 588,984, now U.S. Pat. No. 4,001,594 and Japanese Patent Application (OPI) No. 471/1972. The application Ser. No. 588,984 discloses a method for measuring the transmission density of a negative to generate an exposure control signal. The method (as shown in FIG. 9 herein) includes: detecting the highest density and the lowest density of a preselected essential portion 3 of the scene 2 of a 35 mm color negative. The center of the scene is regarded as important for the essential portion because a subject of interest is often recorded in the center of the scene; obtaining a difference therebetween to provide a non-linear conversion; and adding said lowest density signal to said non-linear converted density difference (gradation) signal, wherein exposure controlling is performed on the basis of said added signals. Prior to the Ser. No. 588,984 invention it was typical to base the photographic exposure for printing on the average transmittance (transmission) density LATD (large area transmittance density), which was obtained by scanning the entire frame of the negative. However, satisfactory prints were not obtained in the case where the LATD differed greatly from the average density of the essential portion of the negative. According to the Ser. No. 588,984 invention this problem was partially solved by obtaining the density of the essential portion of the negative. The density is obtained by using a contrast value and the lowest density detected; the contrast value being the difference between the highest density and the lowest density detected from the essential portion of the film. According to this method, reasonably satisfactory prints may be obtained from various negatives such as, for example, negatives with subjective density failure, color negatives with subjective color failure, negatives with extremely high gradation or extremely low gradation, and the like, from which it has not been possible to obtain satisfactory prints by way of a conventional exposure controlling method using only the large area transmittance density. However, since the method merely measures the highest and the lowest densities of the essential portion, two negatives having picture patterns which require wholly opposite exposure corrections, e.g., where one is a picture of a person with rear illumination as indicated in FIG. 9A and the other is a picture of a person with front illumination as indicated in FIG. 9C, are forced to undergo the same exposure correction, so that satisfactory prints cannot often be obtained.
The method disclosed in Japanese Patent Application (OPI) No. 471/1972 provides an arrangement, wherein the characteristic values measured are: (1) the highest density of a subject portion of the negative; (2) the average density of an upper peripheral portion of the negative with the exception of the subject portion; and (3) the average density of a lower peripheral portion with the exception of the subject portion. The latter measurements are combined to classify the negative for correcting the exposure by an amount well suited to the negative. This method also provides reasonably satisfactory prints from negatives, such as, a negative with subjective density failure, a color negative with subjective color failure, and the like, as previously described. According to this method, the negatives are classified into three scene groupings: (1) a rear illumination scene (for example, an adverse-light photography); (2) a front illumination scene (for example, a strobo photography); and (3) a normal scene. Classification is made on the basis of "background function" determined by the average densities of the upper and lower peripheral portions. However, this proposes exposure amount correction conditions with respect to the scene assuming that the sky is bright while the ground is dark, and hence, the picture pattern of the negative must be discriminated in light and shade in up and down directions. Therefore, in the case of negatives whose frame has a greater breadth than length, such as 135 Size (Leica) negative or the like, when a picture is taken with a camera placed in a longitudinal position, there is a possibility that the upper portion may not be discriminated from the lower portion, posing a disadvantage that scenes of the image recorded on the negative cannot be classified.
Furthermore, according to the above mentioned method, a snow scene can be classified into the front illumination scene, so that the wholly opposite correction is applied thereto, which is a fatal disadvantage.